The one thing you can say for certain about Twitter is that it makes a terrible first impression. You hear about this new service that lets you send 140-character updates to your "followers," and you think, Why does the world need this, exactly? It's not as if we were all sitting around four years ago scratching our heads and saying, "If only there were a technology that would allow me to send a message to my 50 friends, alerting them in real time about my choice of breakfast cereal."